Classic Projects - the 'Spruce Goose'

By Nick Smith

Published Monday, September 17, 2012

Howard Hughes's H-4 Spruce Goose boat plane was the largest aeroplane ever built. But it flew only once, and for only a minute.

It was supposed to be the aeroplane that would solve the Allies' trans-Atlantic transportation problem. The largest flying boat in history, the H-4 'Hercules' would carry personnel and materiel by air, scuppering the German sea offensive. The problem was that the 'Spruce Goose' as the H-4 became universally known didn't take to the skies until 2 November 1947, when it made its inaugural and only flight. With its designer, eccentric billionaire industrialist and moviemaker Howard Hughes, at the controls, the plane remained airborne for about one mile at an altitude of 70 feet, travelling at a speed of 80mph.

However, Hughes could not claim that the concept of the trans-continental heavy transport seaplane was his. This honour goes to Henry J Kaiser, famed industrialist and builder of 'Liberty' ships, who felt that the sky was a safer way to get men and equipment from the USA to Europe during the war. Kaiser approached aircraft designer Hughes, and by 1942 the US government had given the duo a contract to produce three HK-1 aircraft within two years, along with $18m of federal money (which was later to be supplemented by a further $7m out of Hughes' private wealth.)

Kaiser had a reputation for being able to build ships quickly, and officials hoped that his industrial flair combined with Hughes' aeronautical genius would provide a quick turnaround. But work was slow and a frustrated Kaiser pulled out of the project (at which point the HK-1 was renamed the H-4, as it was Hughes' fourth aircraft design). In fact, the work was so slow that only one finished model was ever completed, two years after hostilities had ended.

In terms of the project's scale though, the world had never seen anything like it. Kaiser called it "the most monumental programme in the history of aviation". He may well have been right, for despite the problems associated with the project, Hughes had built a classic. A'mono-hull with eight wing-mounted engines, the H-4 had the potential to move armoured vehicles, 750 personnel (or 400 stretcher cases on the return flight) from one continent to another in relative safety and out of reach of the German U-boats. It easily dwarfs today's Boeing 747-8 wide-bodied jet airline and is listed in Guinness World Records as the "aircraft with the largest wingspan ever constructed".

The most memorable thing about the H-4 is simply that the entire airframe is composed of laminated wood. This was as a result of wartime restrictions on the use of 'strategic materials' such as aluminium or steel.

During the plane's construction, Hughes licensed and perfected a composite materials process called 'Duramold', a plywood-like series of thin wood laminations permeated with plastic glue, shaped and heated until cured. The result was a material lighter and stronger than aluminium. However, the time-intensive research involved with material development meant that the delivery deadline was hopelessly missed. Hughes was eventually required to speak before the Senate War Investigating Committee to justify the use of government funds.

Despite its successful maiden flight, the Spruce Goose never went into production. From 1947 until his death in 1976, Hughes kept the aircraft prototype ready for flight in an enormous, climate-controlled hangar - the first ever built in the USA - maintained by a team of 300 at a cost of $1m per year. Today, the Spruce Goose is housed at the Evergreen Aviation Museum in McMinnville, Oregon.